move stretchy signals from overlay to stretchy itself

Also add overridable opened/closed hooks.

subiquitycore/ui/stretchy.py

@@ -51,7 +51,10 @@
 from subiquitycore.ui.container import ListBox, Pile
 
 
-class Stretchy:
+class Stretchy(metaclass=urwid.MetaSignals):
+
+    signals = ['opened', 'closed']
+
     def __init__(self, title, widgets, stretchy_index, focus_index):
         """
         title: goes in the LineBox
@@ -64,6 +67,13 @@ def __init__(self, title, widgets, stretchy_index, focus_index):
         self.stretchy_index = stretchy_index
         self.focus_index = focus_index
 
+    def opened(self):
+        """Called when the stretchy is placed on the screen."""
+        pass
+
+    def closed(self):
+        """Called when the stretchy is removed from the screen."""
+
     @property
     def stretchy_w(self):
         return self.widgets[self.stretchy_index]
@@ -73,8 +83,6 @@ class StretchyOverlay(urwid.Widget):
     _selectable = True
     _sizing = frozenset([urwid.BOX])
 
-    signals = ['closed']
-
     def __init__(self, bottom_w, stretchy):
         self.bottom_w = bottom_w
         self.stretchy = stretchy

subiquitycore/view.py

@@ -18,7 +18,11 @@
 Contains some default key navigations
 """
 
-from urwid import Overlay, Text
+from urwid import (
+    emit_signal,
+    Overlay,
+    Text,
+    )
 
 from subiquitycore.ui.container import (
     Columns,
@@ -60,12 +64,14 @@ def show_overlay(self, overlay_widget, **kw):
         self._w = Overlay(top_w=top, bottom_w=disabled(self._w), **args)
 
     def show_stretchy_overlay(self, stretchy):
+        emit_signal(stretchy, 'opened')
+        stretchy.opened()
         self._w = StretchyOverlay(disabled(self._w), stretchy)
-        return self._w
 
     def remove_overlay(self):
         if isinstance(self._w, StretchyOverlay):
-            self._w._emit('closed')
+            emit_signal(self._w.stretchy, 'closed')
+            self._w.stretchy.closed()
         # disabled() wraps a widget in two decorations.
         self._w = self._w.bottom_w.original_widget.original_widget